The East Side Gallery is a 1.3 km stretch of the Berlin Wall along Mühlenstraße and the river Spree in Friedrichshain / Kreuzberg which has, since 1990, been the canvas for 105 paintings by artists from all over the world, making it a most interesting open-air gallery depicting scenes and messages of positivity, unification, and joy, not just for Berlin in the wake of the fall of the Berlin Wall, but for the wider world.
Although the majority of the paintings have been tainted by graffiti and damaged by natural erosion, it's a very nice stretch to saunter and take in the messages and artworks on display. Behind the wall also offers glimpses of work by 'opportunistic' artists using the rear of the wall as their canvas' and there are green spaces along the river where Berliners chill out, have a relaxing beer or picnic as river cruise boats pass up and down the Spree. You can see the East Side Gallery as part of the Free Alternative City Tour recommended by Freetour.com.
Hint: Continuing passed the East-Side Gallery, taking a left onto An der Schillingbrücke, brings you to Yaam – a reclaimed space by the river which has been converted into a very cool little beach club. It's an Afro-Caribbean collective which includes volleyball & basketball courts, a man-made beach with bar and seating, live music and DJs as well as Afro-Caribbean street-food, stalls selling art and goods and just a very happy, chilled out vibe – a great place to sip a cold beer and bop your head to tunes in the Summer sun.